Provided is an apparatus and method for detecting fraudulent passwords so that computer break-in attempts can be distinguished from authorized users incorrectly entering their passwords. The second processing unit is selectively inactivated and activated under control of the first processing unit to reduce power consumption in the second processing unit. Measurement gate start and end positions are set relative to the multiple signal transitions based on the received signal transition data. In the disclosed embodiment, 4 columns share a common multiplexed column buffer.